In automobiles with an automatic transmission, it is a preferred practice for the operator to apply the service brakes at the time the transmission selector lever is moved from Park position to a Drive range. This practice not only assures that the vehicle is held stationary during this shift, but also assures that the operator's foot is not inadvertently pressing the accelerator pedal. This avoids the consequences of applying power at an unexpected moment. It has been proposed to provide an interlock mechanism to prevent shifting out of Park position unless a brake is first applied.
U.S. Pat. No. 4,473,141 to Mochida shows a shift lever and parking brake control which has a pin on a shift lever movable through a shift gate having a Park position. An electromagnetically controlled plunger spring is biased into the gate to block pin movement into or out of the Park position. The electromagnet is electrically connected in series with a parking brake switch and an ignition switch. This causes the plunger to be withdrawn by the electromagnet to permit shifting between Park and Reverse only when the engine is running and the parking brake is on.
U.S. Pat. No. 3,994,183 to Markl shows an electromagnetically controlled lock for a shift selector which is released for operation when ignition is turned on. A brake interlock is not included in this disclosure.
A brake-transmission interlock has been used in Audi production automobiles. In that case, a pin on a shift lever movable through a shift gate having a park position (similar to Mochida) is blocked from leaving the Park position by a solenoid operated blocking member in the path of the pin. The blocking member is pivotally mounted on the same axis as the shift lever for movement between blocking and release positions. A solenoid, actuated only when the service brake is released moves the blocking member to a blocking position and when the brake is applied a spring moves the member to a noninterfering position.